The United States says it expects to pass another round of tough sanctions against Russia over its alleged involvement in the conflict in eastern Ukraine. In an interview with VOA, the US Ambassador to Ukraine Geoffrey Pyatt said Russian President Vladimir Putin must take steps to de-escalate the crisis.

The shooting down of a Malaysia Airlines passenger jet on July 17th thrust the conflict in eastern Ukraine onto the agenda of governments around the world.

In an interview with VOA, US Ambassador to Ukraine Geoffrey Pyatt says all evidence continues to suggest Russian-made weapons downed the plane.

“We have high confidence that Malaysia Flight 17 was brought down by an SA-11 missile, fired from territory controlled by the separatists. We know that these missile systems have moved back into Russia. The only fact that we don’t know at the moment is who pressed the button," said Ambassador Pyatt.

Moscow and the rebels deny involvement.

The Russian-backed separatists have given investigators very limited access to the crash site.

Ambassador Pyatt says just one phone call from President Putin would force the rebels to allow access.

“Critical to remember also that many of the leaders of the so-called Donetsk People’s Republic are in fact Russian citizens, they’re Russian passport holders. Several of them are Russian intelligence operatives," he said.

Russia continues to deny providing any material support for the separatists. Ambassador Pyatt says the latest US intelligence paints a very different picture.

“Clearly a pattern of escalating behavior from Russia. Concerned also about the persistence of these training camps in the Rostov (border) region. The evidence that additional and more advanced weapons systems are being mobilized around these training camps, perhaps in preparation for being transferred into Ukraine," said Pyatt.

A recent report from Human Rights Watch warns of mounting civilian casualties caused by firing from both government and rebel forces. The U.S. Ambassador says so far the Ukrainian army has shown restraint.

“We hope very much that President Poroshenko will stand by his commitment that there will be no urban offensives, there will be no urban warfare in Donetsk or any of the major cities of the Oblast," he said.

The United States has applied sanctions to key Russian individuals and businesses, including the financial, energy and defense sectors.

Ambassador Pyatt says it’s vital that allies in Europe move in step.

“Our sanctions have been effective up until this point precisely because they’ve been coordinated closely with Europe. Working to send a consistent and clear international message that Russia needs to respect the security order of Europe and that Russia needs to respect Ukraine’s territorial integrity," he said.

Russia’s Foreign Minister Sergei Lavrov said Russia was disappointed by the sanctions - but says it will not retaliate or as he put it ‘fall into hysterics.’